[R] problem in while loop?
Amen Alyaari
amen.alyaari at bordeaux.inra.fr
Fri Aug 30 14:24:40 CEST 2013
Thanks Berend.
Yes that is right. I should get 5 values(results) of x_e because I have
five values of X. I wonder how can I fix it?
On 30/08/2013 13:13, Berend Hasselman wrote:
> On 30-08-2013, at 09:44, Jonsson<amen.alyaari at Bordeaux.inra.fr> wrote:
>
>> I have three datasets that I want to compute the errors between them using
>> linear regression.for this, I want to iterate to reach certain criteria for
>> the calibration. if changes become smaller than eps the iteration is
>> successful, hence stop and write parameters into cal:eps=0.00001 if number
>> of iterations is> itermax the iteration failed, hence stop and fill cal
>> with missing value itermax=400
>>
>> So I tried this code:
>>
>> x= c(5,2,4,2,1)
>> y= c(5,3,4,6,9)
>> z= c(5,8,4,7,3)
>> itermax=400
>> get initial calibration parameters, here we assume that:x is the reference
>> dataset offset x_a=0, slope x_b=1 the other two datasets y, z are
>> "calibrated" to x using a simple linear regression
>>
>> res=lm(x~y)
>> y_a=coef(res)[1] ; y_b=coef(res)[2]
>> res1=lm(x~z)
>> z_a=coef(res1)[1] ; z_b=coef(res1)[2]
>> y_t = y/y_b - y_a/y_b # "calibrate" y
>> z_t = z/z_b - z_a/z_b #"calibrate" z
>> x_e = sqrt(mean((x-y_t)*(x-z_t)))#calculate error of x
>> iter<- 0
>> while(((x_e-x)> 0.00001)&& (iter< itermax)) {
>> iter<- 0 ##start iteration
>> x = x_e
>> res=lm(x~y)
>> y_a=coef(res)[1] ; y_b=coef(res)[2]
>> res1=lm(x~z)
>> z_a=coef(res1)[1] ; z_b=coef(res1)[2]
>> y_t = y/y_b - y_a/y_b # "calibrate" y
>> z_t = z/z_b - z_a/z_b #"calibrate" z
>> x_e = sqrt(mean((x-y_t)*(x-z_t)))
>> iter<- iter + 1 # increase iteration counter
>> }
>> But I got the same result for X_e before and after the loop:
>>
>>> x_e
>> [1] 6.454089
>>
> I tried your code and got this error message:
>
> Error in model.frame.default(formula = x ~ y, drop.unused.levels = TRUE) :
> variable lengths differ (found for 'y')
> Calls: lm -> eval -> eval -> <Anonymous> -> model.frame.default
>
> And looking at your code: x is a vector, x_e is a scalar and in the while loop you are assigning x_e to x so x is then a scalar.
>
> Berend
>
--
Amen Alyaari, UPMC
PhD student
Unit of Functional Ecology& Environmental Physics [EPHYSE]
National Institute of Agricultural Research [INRA].
71, Avenue Edouard Bourlaux
33140 Villenave d'Ornon
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